1. Field of the Invention
The present invention generally relates to the field of door openers and, more particularly, to a drive device for a hatch of a motor vehicle.
2. Description of the Related Art
Conventional drive devices for the hatch of a motor vehicle typically include a first fastening element that can be connected to a stationary component or to a movable component and a housing tube that is located at an end of the drive device opposite to the first fastening element. The housing tube is able to move axially relative to the first fastening element and has a second fastening element on the end opposite the first fastening element, where it is possible to connect this second element to the movable component or to the stationary component.
The drive device also includes a spindle drive that comprises a threaded spindle and a spindle nut that is mounted on the threaded spindle. The spindle drive permits the first fastening element and the housing tube to be driven axially relative to each other. In addition, the spindle drive can be rotatably driven by an electric motor, where the output shaft of the motor can rotate the threaded spindle or a connecting component of a clutch.
In such conventional drive devices, it is known that the threaded spindle can be designed with a thread which has the same lead over the entire length of the spindle. As a result, the shifting device exerts the same shifting force over the entire shifting stroke.
It is therefore apparent there is need for a drive device of the above-indicated type which can produce different shifting forces over the enter course of the shifting stroke in a simple manner.